1. Field of the Invention
The present invention relates generally to the contacting of fluids and particulate materials. Specifically, this invention relates to the internals of reactors used in the contact of fluids and solid particles. More specifically, this invention relates to the design of novel connectors for use in radial flow processes and apparatuses.
2. Description of the Related Art
A wide variety of industrial applications involves radial or horizontal flow apparatuses for contacting a fluid with a solid particulate. Representative processes include those used in the refining and petrochemical industries for hydrocarbon conversion, adsorption, and exhaust gas treatment. In reacting a hydrocarbon stream in a radial flow reactor, for example, the feed to be converted is normally at least partially vaporized when it is passed into a solid particulate catalyst bed to bring about the desired reaction. Over time, the catalyst gradually loses its activity, or becomes spent, due to the formation of coke deposits on the catalyst surface resulting from non-selective reactions and contaminants in the feed.
Moving bed reactor systems have therefore been developed for continuously or semi-continuously withdrawing the spent catalyst from the catalyst retention or contacting zone within the reactor and replacing it with fresh catalyst to maintain a required degree of overall catalyst activity. Typical examples are described in U.S. Pat. Nos. 3,647,680, 3,692,496, and 3,706,536. In addition, U.S. Pat. No. 3,978,150 describes a process in which particles of catalyst for the dehydrogenation of paraffins are moved continuously as a vertical column under gravity flow through one or more reactors having a horizontal flow of reactants. Another hydrocarbon conversion process using a radial flow reactor to contact an at least partially vaporized hydrocarbon reactant stream with a bed of solid catalyst particles is the reforming of naphtha boiling hydrocarbons to produce high octane gasoline. The process typically uses one or more reaction zones with catalyst particles entering the top of a first reactor, moving downwardly as a compact column under gravity flow, and being transported out of the first reactor. In many cases, a second reactor is located either underneath or next to the first reactor, such that catalyst particles move through the second reactor by gravity in the same manner. The catalyst particles may pass through additional reaction zones, normally serially, before being transported to a vessel for regeneration of the catalyst particles by the combustion of coke and other hydrocarbonaceous by-products that have accumulated on the catalyst particle surfaces during reaction.
The reactants in radial flow hydrocarbon conversion processes pass through each reaction zone, containing catalyst, in a substantially horizontal direction in the case of a vertically oriented cylindrical reactor. Often, the catalyst is retained in the annular zone between an outer particle retention device (e.g., an inlet screen) and an inner particle retention device (e.g., an outlet screen). The devices form a flow path for the catalyst particles moving gradually downward via gravity, until they become spent and must be removed for regeneration. The devices also provide a way to distribute gas or liquid feeds to the catalyst bed and collect products at a common effluent collection zone. In the case of radial fluid flow toward the center of the reactor, for example, this collection zone may be a central, cylindrical space within the inner particle retention device. Regardless of whether the radial fluid flow is toward or away from the center, the passage of vapor is radially through one (outer or inner) retention device, the bed of catalyst particles, and through the second (inner or outer) retention device.
Radial flow reactor design typically requires that the pressure drop across the vessel be minimized. This requires the use of large diameter inlet and outlet nozzles. Two typical, but non-limiting, radial flow reactor configurations include a top inlet, inward radial flow reactor and a top inlet, outward radial flow reactor. Both reactor configurations may include an elbow connector, which joins the central conduit to the inlet nozzle (for outward radial flow), or the outlet nozzle (for inward radial flow). The requirement for large diameter nozzles necessitates a restricted space between the interior surface of the vessel wall and the outside diameter of the elbow connector joining the nozzle to the central conduit.
In order to inspect and maintain the vessel, a worker must be able to physically enter the vessel and then disconnect the elbow connector from the nozzle and central conduit. This type of maintenance is a challenge for typical radial flow reactor designs as a miter elbow needs to be removed from the reactor to access the inside of the center pipe, requiring disconnection (for example, by removing flange bolts or vessel shell welds) and removal of the upper portion of the vessel, which involves considerable downtime and expense. Therefore, one problem in the art is how to design radial flow reactors in order to improve accessibility during construction and maintenance of the vessels. Further, the mitered elbows in traditional radial flow reactors limit the possible location of vertical connecting flanges of the vapor transfer line, which in turn limits the possible locations of other reactor internals, such as, the transfer pipes.